My husband and I didn't always agree about what to do when our son lived with us. So usually I waited and in time my son would do something so awful or destructive that it was a no brainer to kick him out. After that happened twice, I just took a stronger stance and I called the shot. My husband didn't quarrel with me about it because I think he knew it would be futile.
Take your stand, be strong, and set boundaries. Let your husband know what you are doing and if it's time for your son to leave, then it's time for your son to leave...before the chaos begins.
It very hard to be a mama of an addicted child, but we don't have to let the darkness of addiction drag us down too. "Let go or be dragged" is one of my favourite sayings here because it spells it out loud and clear.
Hugs from my heart to your.